| The Bt transgenic cotton (Bt cotton in short) is high-effective for keeping cotton bollworm Helicoverpa armigera (Hiibner), an important worldwide agricultural insect pest, under control, as the growing area of Bt cotton has been increasing rapidly, the development of resistance to Bt in H. armigera become a decisive problem that should not be overlooked. In this dissertation, by using several Bt resistant strains of H. armigera systemically selected for more than five years by the author, the detecting methods for determining the resistance levels were compared, the fecundities of Bt resistant strains and the survivals of their progenies were tested, the Bt toxin receptor proteins - APNs (aminopeptidases N) in the midgut of H. armigera were separated and purified, five genes encoding APN proteins belong to three types were cloned and sequenced, and the binding kinetics between CrylA toxin and BBMV (brush border membrane vesicle) of H. armigera in resistant/susceptible strains were analysed. It is the first time to study the Bt resistance mechanism of H. armigera so far in China. The results were as follows:After selected for 46 generations, the relative resistance ratios of//, armigera to Bt insecticide, Bt protoxin and Bt cotton were up to 1083.33, 417.00 and 48.67 times respectively as many as that of sensitive strains. When the resistance level was rather low, the data of larval mortality could be used to compare the differences among cotton bollworm strains; as the resistance level was more higher, most of the poisoned larvae were still alive, i.e. the larval mortality can not objectively reflect the susceptibility of H. armigera to Bt, so the larval body-weight was used by the author to substitute for larval mortality, because there is significantly negative correlation between body-weight and poisoning level of larvae.In comparison with susceptible strain, the larval survival and body-weight of H. armigera feeding on the diets containing Bt insecticides that having high level resistance to Bt increased significantly, while its copulation rate and fecundity of adults, and hatching rate of eggs were decreased obviously, and the oviposition stage was shortened markedly, and those parameters of the crosses between resistant andsusceptible strains were evidently higher than self crosses of resistant lines, and the larval survivals of the former were obviously increased than that of susceptible strains.By using Mg/EGTA method, to centrifuge with different speeds, the BBMV in midgut of H. armigera could be successfully separated, and most of the APN activities in BBMV were preserved. The CHAPS can enhance the dissolution of BBMV, and PI-PLC can cleave the APN from midgut membrane, the combination of Mono-Q and FPLC methods can purify partial APN. The results of Western blotting showed that the 120 and 170kDa proteins were the main ones that bound Cry 1 Ac in the BBMV, and the protein at 120kDa was the APN anchored by GPL By using ligand blotting test, a 120kDa protein in BBMV was recognized binding with 5I-Cryl Ac, it was reconfirmed that the 120kDa APN is the receptor for Cry 1 Ac.By using 125I-labeled Bt toxin, the differences of binding kinetics among CrylAa, CrylAb, Cry 1 Ac and BBMV in larval midgut of resistant and susceptible H. armigera were tested. After the saturation test and homologous/heterologous competition and dissociation assays, it was found that the combination of BBMV and Bt toxin protein was related in a certain degree to Bt toxicity, while there was no direct relationship between the activity of APN and Bt resistance. The occurrence of resistance to Cry 1 Ac in H. armigera is probably related to the decrease of binding-site number of BBMV and Cry 1 Ac. Nevertheless, it looks as if there will be not only the receptor protein, but also the other factors are related to Bt resistance. It was presumed that there is a common binding-site for CrylAa, CrylAb and Cry 1 Ac, and other one for CrylAa only.By designing the degenerate primers and using RT-PCR and RACE methods, 5 genes e...
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